Within the past few years, seat cushions fabricated from high-resiliency polyurethane foams have gained increasingly wide acceptance. The polyurethane foams in such cushions are usually made by reacting a polymer/polyol composition and another polyol with organic polyisocyanate in the presence of catalysts, a blowing agent and a silicone surfactant. The polymer/polyol compositions most widely used in producing such polyurethanes consist essentially of a major amount of a polyol and a minor amount of a polymer. The polyols in these polymer/polyol compositions are typically polyoxypropylenepolyoxyethylene polyols wherein the polyoxyethylene blocks endblock at least 35 mole percent of the polyoxypropylene blocks and are terminated with primary hydroxy groups. These polyols usually have about 85 weight percent polyoxypropylene blocks and about 15 weight percent polyoxyethylene blocks and have hydroxyl numbers of about 34, about 2.6 hydroxyl groups per molecule and about 70 mole percent primary hydroxyl groups. Seat cushions fabricated from polyurethane foams made from formulations containing such polymer/polyol compositions have outstanding properties, particularly excellent load-bearing properties.
Although the above-described polyurethane foams have outstanding properties, there is still some room for improvement in their properties, particularly when intended for use in seat cushions that may be subjected to certain conditions. By way of illustration, seat cushions fabricated from such polyurethane foams tend to exhibit a phenomenon known as "static fatigue". Thus, when an individual is seated on the cushion for a prolonged period of time, the cushion tends to become deformed and to retain the deformation to some extent after the load imposed by the individual is removed. As a further illustration, seat cushions fabricated from such polyurethane foams tend to lose their desirable load-bearing properties to some extent when exposed to conditions of high humidity for prolonged periods of time.